The goals of this proposal are to understand the immunobiologic relevance o a unique subset of T cells (called dendritic epidermal T cells, or DETC) which populate the skin of all normal mice, and to understand their relationship(s) to the T cells present in normal and diseased human skin. The unique features of DETC (e.g., homogeneity of their V-gamma5/V-delta1+ T cell receptors (TCRs), apparent restriction in adult mice to the skin, and capacity to recognize a ligand expressed on stressed epidermal cells), have led to the hypothesis that they play distinctive roles in cutaneous immune surveillance and/or immunoregulation; postulated (but unproven) roles include early responses to intracellular infection, elimination of altered/stressed cells, down-regulation of responses mediated by conventional TCRalpha-beta cells, and perhaps even initiation of autoimmunity. The specific aims of this proposal include: 1) In vivo examination of such potentially relevant biologic roles of DETC in cutaneous immunity and/or immunopathology by developing homologous recombinant mice selectively deficient in V-gamma5+ DETC and then testing such DETC-deficient mice in several model systems, including induction and growth of skin tumors, allergic contact dermatitis, and experimental cutaneous autoimmune disease. 2) Definition of factors affecting the localization/proliferation of DETC in the skin. Strategies include attempts to reconstitute the skin of DETC-deficient mice with DETC-like cells from newborn liver, and studies of the role(s) of anagen hair follicles in these processes by analysis of DETC density/heterogeneity in the skin of various hair mutant mice and by localization of fluorescein- labeled fetal thymocytes. 3) Characterize the ligands which activate DETC and the molecules involved in such activation. Strategies include analysis of a broad range of normal and transformed cells/lines from various tissues for their abilities to stimulate DETC proliferation and IL-2 secretion in vitro, use of alpha-heat shock protein Abs or Abs to various adhesion/accessory molecules expressed by DETC (such as CD45, CD8, LFA-1, CD28) to try to block such responses, and preparation of a monoclonal Ab directed against the DETC V-gamma5/V-delta1+ TCR ligand on stressed epidermal cells in order to purify the relevant stimulatory molecule(s). 4) Analysis of the functional heterogeneity of DETC. Strategies include examining accessory molecule expression on DETC in different activation states (freshly isolated vs lines/clones maintained under distinct culture condition) and correlating these patterns with DETC proliferation, lymphokine secretion and cytotoxicity profiles, as well as examining the lymphokine and cytotoxicity profiles of freshly isolated and cultured DETC from normal and IL-2-deficient mice (homologous recombinants or HSV-thymidine kinase transgenics) cultured with such cytokines as IL-2, IL-4 or IL-7. Such studies should advance understanding of gamma-delta cell/skin interactions under physiologic and pathologic circumstances in mice and in man.